Coating having solar control properties for a substrate, and method and system for depositing said coating on the substrate

ABSTRACT

The present invention relates to coating glass for architectural or automotive use, either monolithic or laminated, having solar control properties. The coating consists of several layers of different metal oxide semiconductors (TiO 2 , ZnO, ZrO 2 , SnO 2 , AlO x ) and a layer of metallic nanoparticles, which when superimposed on a pre-established order give the glass solar control properties. In particular the use of protective layers of n-type semiconductors around the metallic nanoparticles layer. It also relates to the method for obtaining the coating by means of the aerosol-assisted chemical vapor deposition technique, using precursor solutions containing an organic or inorganic salt (acetates, acetylacetonates, halides, nitrates) of the applicable elements and an appropriate solvent (water, alcohol, acetone, acetylacetone, etc.). The synthesis is performed at a temperature between 100 and 600° C. depending on the material to be deposited. A nebulizer converts the precursor solution into an aerosol which is submitted with a gas to the substrate surface, where due to the temperature the thermal decomposition of the precursor occurs and the deposition of each layer of the coating occurs.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/435,252, filed Apr. 13, 2015, which is a national stage applicationof International Patent Application No. PCT/MX2013/000127, filed Oct.11, 2013, which claims benefit of Mexican Patent Application No.MX/a/2012/011948, filed Oct. 12, 2012, each of which are incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to coatings with solar control propertiesdeposited on glass intended for architectonic or automotive use, eithermonolithic or laminated; and to a method and system for depositing saidcoatings by the aerosol-assisted chemical vapor deposition technique(AACVD).

BACKGROUND OF THE INVENTION

Glass used in buildings and vehicles, generally protects us from theenvironment (rain, wind, noise, etc.), allowing more pleasant conditionsinside. However, ordinary glass does not protect us from solarradiation, since it only absorbs some of the UV radiation, reflecting atotal of about 7% and transmits most of the entire solar spectrum. Inparticular, in the case of automobiles, the trend is to use larger areaand more inclined (relative to the horizontal) (front) windshields, thussubstantially increasing the amount of incoming solar radiation,reaching about 35% of total heat entering the vehicle, which correspondsto ˜50% of heat input only through the windshield. This requiresimprovements in the properties of glass (by coating) to reduce infraredinput improving passenger comfort, increasing the service life of thevehicle interior furnishings (console, carpets, etc.) and reducing theuse of air conditioning thereby saving fuel; this is what is known assolar control.

Value added to glass or other products may be increased depending on thefunctional properties conferred to its surface or some coating depositedon it. Many phenomena that give functional characteristics to a materialoccur on the surface or in a region close to it. It is thereforepossible to coat economical substrates (glass) with functional materialsin the form of thin layers. Thus, the resulting product has thefunctional property of the coating and the characteristics of thesubstrate, particularly those of glass.

Solar control refers to the ability to change the amount of transmittedor reflected radiation, in the near-UV (UV; 300-380 nm), visible (VIS;380-780 nm) and infrared (IR; 780-2500 nm) spectral ranges. Lowtransmittance is generally pursued in UV and IR ranges, while the VIStransmittance may be high (>70%) or low, depending on the application.

In addition to blocking infrared radiation, glass and its coatings musthave other properties, such as: high transmittance in the visiblespectrum (>70%), high mechanical strength, chemical resistance andweather resistance, they must be able to undergo thermal treatments(tempering, bending), must show a neutral color without iridescence, lowdispersion (haze) and be low cost. The aggregate of necessary propertiesmakes the development of this type of coatings a technically complex andvery difficult problem.

There are many alternatives to obtain solar control properties. This isreflected in the myriad of scientific papers, patents and patentapplications existing on the subject. For example, one scientificpublication referring to coatings with solar control properties, is thepaper “Solar heat reflective glass by sol-gel nanostructured multilayercoatings” by Z. Nagamedianova and colleagues, published in the journalOptical Materials in 2011, Volume No. 33, pages 1999-2005 describingcommercial clear glass coated by the sol-gel method with three layers ofoxides, TiO₂—SiO₂—TiO₂, which have the property of reflecting the IRC(near-IR). Transmittance in the VIS>70%, high UV blocking (Tuv<35%) andhigh reflectivity (>60%) in the 800 to 950 nm range are reported.

Regarding patents, U.S. Pat. No. 5,242,560 “Heat treatablesputter-coated glass” by Guardian Industries Corp. describes a coatedglass that may be heat treated by sputtering, consisting of a layer ofNi alloy with one or two layers of Sn oxide, and optionally anintermediate Al layer.

The published US Patent Application No. 2011/0236715 A1 relates to a“Solar control coating with discontinuous metal coating layer” owned byPPG Industries Ohio, Inc. Said application proposes a coating depositedon at least a portion of a substrate, comprising multiple dielectriclayers alternating with multiple metal layers, with at least one of themetal layers comprising a discontinuous metal layer.

In British Patent (1971) No. 1241889 “Heat reflecting glass and methodfor manufacturing the same” owned by Asahi Glass Co., a glass substratewhich reflects heat and transmits visible light, comprised by acomposite of a metal oxide layer (TiO₂, Ta₂O₅, WO₃, ZrO₂, Nb₂O₅, ThO₂,SnO₂) of higher index than glass, in which microscopic particles ofmetallic Pd or Au are immersed, is claimed. The proposed method issimilar to Sol-gel.

Furthermore, there are several methods of synthesis of coatingsincluding: sol-gel, pulsed laser deposition, vacuum evaporation,electron beam, sputtering, CVD and plasma discharge, which includes thevariant called AACVD. Among these preparation techniques, the AACVDmethod has some advantages such as: its simplicity and low cost ofimplementation, since it needs no sophisticated equipment, ability tooperate at atmospheric pressure and it is scalable to industrial level.This technique allows obtaining coatings with several advantages: a)controllable composition, even when changing the composition of aprecursor solution during deposition with the purpose of obtainingmaterials with a concentration gradient, b) good adhesion, c) uniformand controllable thickness over a wide range, d) ease of production ofcomposite materials or multiple layers e) it can be applied fordepositing coatings on flat substrates or on inner or outer pipesurfaces, f) finally the properties of the materials obtained arecomparable to those of materials deposited by other more sophisticatedtechniques such as reactive sputtering, reactive evaporation, PLD, etc.which require expensive high vacuum systems, radio frequency sources,gas control, power laser, etc.

The AACVD method is a physical chemical hybrid process for obtainingcoatings. It consists in producing a cloud of micrometric drops, from asolution composed of organometallic precursors or inorganic compounds,dissolved in a particular solvent for each type of compound (water,alcohol, acetone, acetylacetone, etc.). The aerosol can be generated bypneumatic, electrostatic or ultrasonic methods. The aerosol precursorsolution must be transported to the deposition area by a carrier gas. Inthe deposition area is the glass substrate, which is heated to aspecific temperature depending on the material to be deposited or theprecursors used. In the deposition area, as the cloud approaches thesubstrate it warms up causing initially solvent evaporation, fusion,evaporation or possible sublimation or thermal decomposition of theprecursor compound, its diffusion towards the glass surface; where theprocess continues with the adsorption of the reactants, the chemicalreaction, and its evacuation away from the surface.

Some scientific publications referring to systems for production of thincoatings by the AACVD method are:

The paper “Aerosol-Assisted Chemical Vapor Deposited Thin Films forSpace Photovoltaics” by Aloysius F. Hepp et al, published by NationalAeronautics and Space Administration NASA/TM-2006-214445 describingdifferent reactor designs at atmospheric pressure and low pressure,analyzing their main parameters determining the deposition of thinsemiconductor coatings based on In and Cu sulfides for photovoltaicapplications. The area of application of these coatings differs fromthose proposed in the present invention.

Another report “Synthesis, structural characterization and opticalproperties of multilayered Yttria-stabilized ZrO₂ thin films obtained byaerosol assisted chemical vapour deposition” by P. Arnézaga-Madrid, W.Antúnez-Flores, L Monárrez-Garcia, J. González-Hernández, R.Martínez-Sánchez, M. Miki-Yoshida, published in the journal Thin SolidFilms in 2008 with number 516, pages 8282-8288, describes how to obtainmultilayer coatings of yttria-stabilized zirconia on borosilicate glasssubstrates by the AACVD method. The paper discusses the influence ofvarious synthesis conditions such as: concentration of the precursorsolution, substrate temperature, carrier gas flow, etc., on the coatinggrowth rate. The multilayer structure obtained due to the iterativeprocess used allows modulating the refractive index, thus modifying thereflection of the coating.

There are also patents which relate to CVD (chemical vapor deposition)systems for production of thin films on flat substrates, for example,U.S. Pat. No. 6,190,457 B1 describes a horizontal CVD system forobtaining a thin film semiconductor compound made up of two or morecomponents on the surface of a flat substrate. The CVD system has acylindrical reactor and a flat substrate is placed inside the reactor.The reactor has a gas supply section and a section for its disposal.Inside the reactor there are three divisions; in the first two divisionsa gas mixture made up by one that includes the precursor compounds andanother diluent gas. In the third section only an inert gas is fed whichtransports the two previous mixtures.

The U.S. Pat. No. 7,011,711 B2 presents a vertical system using themethod of chemical vapor deposition for producing a thin film on one ormore flat substrates. The system comprises a reactor including avertical pipe and a reaction chamber located inside the pipe. The flatsubstrate is placed at the end of the reaction chamber. Gas input andexhaust is carried out vertically. Throughout the length of the pipe,partition arrangements are positioned to direct the path of the reactiongases and to evacuate the gases produced after the reaction.Additionally, heaters are connected to the vertical pipe that cancontrol the temperature difference between the substrate and the reactorwalls.

Considering the aforementioned technique, the present invention relatesto a coating with solar control properties deposited on glass intendedfor architectural or automotive use, either monolithic or laminated. Thecoating consists of several layers of different metal oxidesemiconductors (TiO₂, ZnO, ZrO₂, Al₂O₃) with different refractive index(n), and a layer of metal nanoparticles (Au, Ag). The layer of metalnanoparticles increases IR blocking. Additionally, the use of n typemetal-semiconductor active junctions, above and below the nanoparticlelayer, allows the injection of negative charges from the metal to thesemiconductor (Schottky junction) protecting it from oxidation and alsopreventing metal agglomeration, to obtain nanoparticles homogeneouslydeposited throughout the coating. The coating component layers aresuperimposed in a predetermined order, such as: glass (VC)/diffusivebarrier (BD)/dielectrics 1 (D1)/n-type semiconductor, adhesive-protector(A)/metal nanoparticles (M)/n-type semiconductor, protector(P)/dielectrics 2 (D2)/mechanical strength (R); thicknesses are selectedso that the coating confers to glass solar control properties,especially a high near-IR blocking (CRI) and high transmittance in theVIS. The number of coating layers may vary being at least three,composed of two n-type semiconductors, distributed below and above thelayer of metal nanoparticles.

The coating was obtained by using the aerosol-assisted chemical vapordeposition technique. This technique uses precursor solutions consistingof a salt containing the element to be deposited, for example titanylacetylacetonate or aluminum acetylacetonate, along with a suitablesolvent such as methanol, ethanol, water or some other solvent forcompletely dissolving the precursor salt. A pneumatic, ultrasonic orelectrostatic type nebulizer converts the precursor solution to a cloudof micrometric drops, which are driven by a carrier gas, usually air,toward the glass surface that is at deposition temperature between 100and 600° C. The particular temperature required depends on the materialto be deposited, in other words, on the precursor used. The process isrepeated successively with the different precursors to deposit all thelayers of the coating.

OBJECTIVES OF THE INVENTION

It is therefore a first object of the present invention to provide acoating with solar control properties and a method and apparatus fordepositing said coating on glass substrates, said coating includingseveral semiconductor layers of different metal oxides (TiO₂, ZnO, ZrO₂,SnO₂ or Al₂O₃), and at least one layer of metal nanoparticles (Au and/orAg, Pt, Pd) to confer to the glass substrate solar control properties.

It is a further object of the present invention to provide a coatingwith solar control properties and a method and apparatus for depositingsaid coating on glass substrates, using, for depositing said coating,the aerosol-assisted chemical vapor deposition technique (AACVD).

A further object of the present invention is to provide a coating andsolar control properties, a method and apparatus for depositing saidcoating on glass substrates, wherein the coating is composed of activen-type protective semiconductor layers deposited one below and the otherone above the layer of metal nanoparticles.

These and other objects and advantages of the coating with solar controlproperties of the present invention will be obvious to those skilled inthe trade, from the following detailed description thereof.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the schematic diagram of a coating with solar controlproperties, comprising a substrate (1), four layers of metal oxides (2),(4), (5), (6) and a layer composed of evenly distributed metalnanoparticles (3).

FIG. 2 shows the schematic diagram of a coating with solar controlproperties, comprising a substrate (7), six layers of metal oxides (8),(9) (10) (12) (13), (14) and a layer composed of uniformly distributedmetal nanoparticles (11).

FIG. 3 shows a diagram of the system used for depositing the differentlayers of solar control coating of the present invention.

FIG. 4 shows the cross section of a typical solar control coating, wherethe different component layers can be seen, particularly the uniformlayer of metal nanoparticles surrounded above and below by theprotective layer of n-type semiconductor.

FIG. 5 shows the spectra percentage of transmittance (% T), reflectance(% R) and absorbency (% A) of a typical solar control coating, with thestructure shown in Example 2(VC/TO₂/Al₂O₃/TiO₂/Nano-Au/TiO₂/Al₂O₃/TiO₂). A vertical arrow indicatesthe position of the absorption peak in the IRC around 1000 nm.

FIG. 6 presents the spectra percentage of transmittance (% T),reflectance (% R) and absorbency (% A) of a typical solar controlcoating, with the structure shown in Example 3(VC/ZnO/ZrO₂/Al₂O₃/TiO₂/Nano-Ag/TiO₂/Al₂O₃/SnO₂). A vertical arrowindicates the position of the reflection peak around 800 run.

FIG. 7 includes a schematic showing the methodology for the preparationof substrates and coating deposition by means of the AACVD technique.

DETAILED DESCRIPTION OF THE INVENTION

The present invention describes coatings with solar control propertiesdeposited on glass for architectural or automotive use, eithermonolithic or laminated. Solar control refers to the ability to modifythe amount of transmitted, reflected and absorbed solar radiation in thesolar range comprised between 300 and 2500 nm. Generally lowtransmittance is pursued in the UV and IRC (near-IR) ranges, whiletransmittance in the VIS should be high (>70%) for automotiveapplications or low for architectural applications. The coating iscomposed of two or more layers of different semiconductor metal oxides(TiO₂, ZnO, ZrO₂, SnO₂ or Al₂O₃) and one or more layers of metalnanoparticles selected from Gold (Au), Silver (Ag), platinum (Pt) andpalladium (Pd), uniform, non-continuous and homogenously distributedover the entire surface of the coated substrate.

As exemplified in FIG. 1, the CS solar control coating of the presentinvention is deposited on a surface of a glass substrate 1 by thetechnique of aerosol-assisted chemical vapor deposition technique(AACVD). In the example shown in FIG. 1, the CS solar control coating isdeposited on at least one surface of the substrate 1. As describedherein, the term “solar control coating” refers to a coating comprisingone or more layers or films that affect the solar properties of thecoated article, but not limited to the amount of solar radiation, forexample, visible, infrared, or ultraviolet radiation. The CS solarcontrol coating can block, absorb or filter selected portions of thesolar spectrum, such as IR, UV and/or visible spectrum.

Examples of CS solar control structures are shown in FIGS. 1 and 2,representing 5 and 7 layer coatings, respectively. In the exampleillustrated in FIG. 1, the CS solar control coating comprises 5 layers:There is substrate (1) on which layer (2), consisting of TiO₂ or ZnO,but mainly TiO₂, is deposited first. Its thickness shall be between 10and 70 nm. This first layer also serves as a support for the metalnanoparticles (3) and further as an active protector, given its n-typesemiconductor character, to prevent oxidation of the nanoparticles, aswell as increase their adhesion. The metal nanoparticles layer (3) isdeposited so that the size of the nanoparticles is less than 30 nm, itsdistribution is uniform and covers a large part of the surface (>80%).The function of the metal layer (3) including Au and/or Ag metals, is toincrease IR blocking by absorption and/or reflection (see FIGS. 5 and6). Subsequently, a second active protective layer (4), consisting ofTiO₂ or ZnO, but mainly TiO₂, whose thickness is similar to the firstprotective layer, i.e. between 10 and 70 nm, is deposited on it, whosefunction is to protect the metal nanoparticles from oxidation. Then oneor more dielectric layers are superimposed, in order to increase solarcontrol properties, in particular to increase transmittance in thevisible range. Therefore, in FIG. 1 layer (5) corresponds to an Al oxide(Al₂O₃); its thickness shall be between 10-150 nm. The final layer (6)corresponds to a mechanically resistant material, such as ZrO₂, SnO₂,TiO₂ or a compound of them, preferably including the stronger material(ZrO₂).

The example illustrated in FIG. 2, schematically shows a CS solarcontrol coating made up by 7 layers. FIG. 2 shows a glass substrate (7)on which the first layer (8) is deposited, corresponding to thediffusion consisting of TiO₂ or ZnO with a thickness between 10-70 nm.Subsequently, layer (9) corresponds to one or more dielectrics, e.g.ZrO₂ or Al₂O₃ or both sequentially deposited, its thickness may bebetween 10-150 nm. Then, the support layer (10) follows, which promotesbetter adhesion of nanoparticles and also plays the role of activeprotector, given its n-type semiconductor character, to preventoxidation of the nanoparticles. Support layer (10) may be composed ofTiO₂ or ZnO, but mainly TiO₂. Its thickness shall be between 10 and 70nm. The layer of metal nanoparticles (11) is deposited so that thenanoparticle size is 8 to 30 nm, with a uniform non-continuousdistribution and covering a large part of the surface (>80%). Thefunction of the metal layer (11) including Au and/or Ag metals, is toincrease the IRC blocking, by absorption and/or reflection. This isapparent in FIG. 5, where the spectra are shown as percent oftransmittance (% T), reflectance (% R) and absorbency (% A) of a typicalsolar control coating (structure of example 2) where a vertical arrowindicates the peak position of IRC absorption. Then a second activeprotective layer (12), consisting of TiO₂ or ZnO, but mainly TiO₂, whosethickness is similar to that of the first protective layer, i.e. between10 and 70 nm, is deposited on layer (11). The last dielectric layers arethen superimposed, whose function is mainly to increase transmittance inthe visible range. Therefore in FIG. 2, layer (13) corresponds to one ormore dielectrics, for example Al₂O₃, whose thickness is similar to thatof the first Al₂O₃ layer, that is, between 10-150 nm and otherdielectrics such as TiO₂, with thickness between 10-120 nm, may be addedon it. The final layer (14) is resistant to abrasion, for example ZrO₂,SnO₂, TiO₂ or a compound of them, preferentially including the strongermaterial (ZrO₂).

These properly deposited structures, with the required thickness, conferto glass solar control properties, particularly IR blocking and adequatetransmittance in the VIS. In particular the use of active n-typemetal-semiconductor junctions, allows injection of negative charges fromthe semiconductor to the metal (Schottky junction) protecting it fromoxidation and also preventing its agglomeration; this allows obtaininguniform layers of homogeneously distributed metal nanoparticles over alarge portion of the solar control coating intermediate surface.

Additionally, it is intended that the developed product has highmechanical, thermal and chemical resistance, sufficient to support themanufacturing processes of tempered and/or laminated glass withoutmaking changes that impair the performance of solar control. The coatedproducts were subjected to various tests to determine industrialtempering capability by means of fracture tests, laminating (Pummeltests and boiling under customer standards and ANSI/SAE Z26.1-1996) andchemical contact resistance of samples to acid solutions. Coated glassessuccessfully passed all of these tests, confirming the feasibility ofintegrating the developed product to tempering and laminating glassmanufacturing processes.

Obtention of Glasses with Solar Control

The aerosol-assisted CVD method (AACVD) is an economical, efficient anduseful process for obtaining relatively thin coatings, with maximumthickness of several micrometers. It consists in producing a cloud ofmicrometric drops, whose diameter is in the range of 1 to 20 mm, from asolution made up by organometallic precursors (acetates,acetylacetonates) or inorganic compounds (halides, nitrates), dissolvedin a particular solvent for each type of compound (water, alcohol,acetone, acetylacetone, etc.). The aerosol can be generated bypneumatic, electrostatic or ultrasonic methods. Among the most effectiveare ultrasonic nebulizers which generate drops with size of a fewmicrometers and with a closed distribution of sizes (FWHM˜10%). In thesenebulizers, a drop cloud is produced by vibration (a few MHz) of apiezoelectric crystal, whose ultrasonic waves are concentrated on thesurface of the solution, which generates the micrometric drop cloud bymeans of cavitation. Droplet size depends primarily on the frequency ofthe piezoelectric (inversely), as well as on surface tension and densityof the solution. Drop size and essentially its size distributiondecisively influences the conditions (substrate temperature, carrier gasflow) of the tank and the quality of the obtained material. A widespreaddrop size distribution prevents optimizing synthesis conditions, becausea large drop requires different conditions to those of a droplet;resulting in an inhomogeneous and shoddy coating. The precursor solutionaerosol must be transported to the storage area by a carrier gas. In thedeposition area, is the glass substrate, which is heated to a specifictemperature depending on the material to be deposited. The substratetemperature is the key parameter controlling the deposition of material.The optimum temperature of the process depends on the precursors used,consequently on the material to be deposited, but in general it can besaid that these are relatively low, between 373 K (100° C.) and 873 K(600° C.). In obtaining a coating, in addition to the thermodynamicconditions it is necessary to verify the kinetics of the process. Sincegrowth of the film depends on: a) the process of transporting thereactant(s) to the vicinity of the substrate surface; where as the cloudapproaches the substrate it warms up initially causing solventevaporation, melting, evaporation or eventually sublimation, or thermaldecomposition of the precursor compound, and thereafter its diffusiontowards the surface. b) kinetic processes on the substrate surface,where the following processes are required in succession: reactantadsorption, diffusion and convergence on the substrate surface, chemicalreaction, diffusion and desorption off the surface of the chemicalreaction products and disposal away from the surface, to avoidcontamination of the deposited material.

Description of the Obtention System:

FIG. 3 shows a schematic diagram of the system used in the process ofthe present invention. The system consists of the following parts:

a) A heating plate or chamber (23) for elevating the temperature of theglass substrate to the deposition temperature between 100 and 600° C.The heating system comprises a temperature control (not shown in thefigure) that allows keeping temperature constant throughout thedeposition process. Moreover, heating shall be uniform throughout theglass surface.

b) A nebulizer (19) which may be of pneumatic, electrostatic orultrasonic type. The carrier gas (16) with its pressure regulator (17)and flow controller (18) and finally the aerosol exit nozzle (20)towards the substrate surface (22).

c) The nozzle drive system of the (21) permits distributing theprecursor solution over the entire surface of the substrate in order toobtain uniform coatings. The nozzle (20) is mounted on the nozzle drivesystem (21) having controlled movement (0.1 to 5 cm) allowing evendistribution of the precursor solution over the whole substrate surface,in order to obtain uniform coatings.

d) The gas extraction system (24) to prevent contamination of thedeposited coating.

Preparation of the precursor solution.

The precursors are mainly organometallic salts of the elements ofinterest and as solvent, one suited to each salt was used, preferablyaqueous or alcoholic solutions were used due to their advantageousfeatures for aspersion (methanol, ethanol, triple distilled water),concentrations used were from 0.001 to 0.2 mol/dm³. Precursors forintroducing dopants were also organometallic salts. Dopant concentrationwill range from 1% atomic up to the solubility limit of the dopantrelative to the base material, which may be up to 10-40% atomic.Complete dissolution of the precursor used by means of suitablestirring, heating and/or ultrasound shall be ensured.

Application Method

The synthesis starts with the preparation of the precursor solutioncontaining an organic or inorganic salt containing the element ofinterest, for example a chloride, nitrate, acetate or acetylacetonate,tin tetrachloride, zinc nitrate, zinc acetate, aluminum acetylacetonate,zirconium acetylacetonate; and a suitable solvent such as methanol,ethanol, acetone, water or a mixture thereof. The concentration of thesolution is in the range of 0.001 to 1.0 mol·dm⁻³.

The substrate (22) is fastened to the heating plate (23). The depositiontemperature between 100 and 600° C. is set, and the substrate system isturned on (22) to stabilize substrate temperature. The remaining partsof the AACVD system are configured: nebulizer (19) and nozzle (20). Thecarrier gas (16) is connected. It is important that the couplings aretight to prevent leakage of aerosol. Additionally the nozzle motionspeed (20) is set between 0.1 and 5 cm/min, which allows varying thethickness of the deposited coatings. Nozzle total travel length is alsoset, depending on the portion of the substrate that is to be covered.The gas extraction system (24) is also turned on to stabilize thetemperature in the entire system.

The introduction of carrier gas (which may be air but depending on thecoating argon, nitrogen or other similar gas may be used) is alsostarted. For thermal stabilization, the flow is set between 1 and 10 Lmin⁻¹. The particular value of the flow of carrier gas and thedeposition temperature depend on the material to be deposited.

Additionally, the precursor solution is introduced in the nebulizer(19). If necessary for long deposition times a larger amount of solutioncan be added during deposition, using a peristaltic pump (15). Acommercial ultrasonic nebulizer (19), operating at 2.4 MHz highfrequency was used in tests.

Upon reaching the thermal stability of the whole system, the processproceeds by turning on the nebulizer (19), generating the aerosol cloudof the precursor solution; simultaneously displacement of nozzle (20)via the nozzle drive system (21) is started. The generated cloud entersthe nozzle (21). In the nozzle, the precursor solution and carrier gasmixture rises in temperature to between 50 and 150° C.; this preheatingto a temperature lower than synthesis temperature ensures that theprecursor reach the substrate surface (22) in the reaction zone at thetemperature required for thermal decomposition and coating deposition iscarried out in optimal conditions. In the substrate surface (22),physical transformations and precursor chemical decomposition arecarried out by action of the temperature, yielding a well bonded, highpurity coating on its surface. Forming of the thin film on the substratesurface occurs after the thermal decomposition of the precursor, forthis reason the surface temperature has a major role in obtaining thematerial of interest. Additionally, changing the nozzle travel speedallows obtaining thin films of different thicknesses.

Once the chemical reaction takes place and reaction gases are generated,they are evacuated by an extraction system (24), to avoid contaminationof the deposited material and thus obtain high purity coatings. Theprocess is repeated with each precursor to deposit all the differentlayers of the coating.

Examples of Coated Substrates EXAMPLE 1

Using a 4 mm-thick clear glass (VC), five coating layers were depositedby the AACVD method with the following structure:

Material Thickness [nm] ZrO₂ 35 Al₂O₃ 45 TiO₂ Nano-Au 75 TiO₂ VC 4 mmOptical properties in this coating solar range are summarized in thefollowing table. Transmittances are presented in the ultraviolet (UV300-380 nm), solar (SOL 300-2500 nm) and visible (VIS 380-780 nm)intervals.

% T UV SOL VIS 43 52 62

EXAMPLE 2

Using a 4 mm-thick clear glass, seven coating layers were deposited bythe AACVD method, with the following structure:

Material Thickness TiO₂ 134 Al₂O₃ 106 TiO₂ 97 Nano-Au TiO₂ Al₂O₃ 101TiO₂ 68 VC 4 mmThe transmittance values at ultraviolet (UV 300-380 nm), solar (SOL300-2500 nm) and visible

(VIS 380-780 nm) intervals of this coating are:

% T UV SOL VIS 36 42 56

FIG. 5 shows the spectra in percentage of transmittance (% T),reflectance (% R) and absorbance (% A) of a typical solar controlcoating, with the structure of Example 2(VC/TiO₂/Al₂O₃/TiO₂/Nano-Au/TiO₂/Al₂O₃/TiO₂). A vertical arrow indicatesthe position of the absorption peak in the IRC around 1000 nm.

FIG. 4 shows the cross section of a typical solar control coating, witha similar structure to Example 2, wherein the glass substrate isrepresented by the number 25; a first layer (26) acting asanti-diffusion barrier (ZnO, ZrO₂); a second layer (27) of a firstdielectric (Al₂O₃, TiO₂, ZrO₂); a third layer 28 of n-typesemiconductor, adhesive-protector (ZnO, TiO₂); a fourth layer (29) ofmetal nanoparticles (Ag, Au, Pt, Pd); a fifth layer (30) of an n-typesemiconductor, protector (ZnO, TiO₂); a sixth layer (31) of a seconddielectric Al₂O₃, TiO₂ or ZrO₂; and seventh layer of materials toimprove mechanical strength selected from SnO₂ or ZrO₂. In said FIG. 4the different component layers, particularly the uniform layer of metalnanoparticles surrounded above and below by the protective layer ofn-type semiconductor, may be seen.

EXAMPLE 3

Using a 4 mm thick clear glass, eight coating layers were deposited bythe AACVD coating method under the following structure:

Material Thickness SnO2 66 Al₂O₃ 249 TiO₂ 86 Nano-Ag TiO₂ Al₂O₃ 114 ZrO₂69 ZnO 54 VC 4 mmThe transmittances at ultraviolet (UV 300-380 nm), solar (SOL 300-2500nm) and visible (VIS 380-780 nm) intervals of this coating are:

% T UV SOL VIS 31 52 63

FIG. 6 presents the spectra in percent transmittance (% T), reflectance(% R) and absorbance (% A) of a typical solar control coating, with thestructure of Example 3 (VC/ZnO/ZrO₂/Al₂O₃/TiO₂/Nano-Ag/TiO₂/Al₂O₃/SnO₂).The vertical arrow indicates the position of the reflection peak around800 nm.

The invention claimed is:
 1. A method for depositing a solar controlcoating on a substrate comprising the steps of: a) placing the substratein a clamping area; b) heating the substrate in a heater chamber to apredetermined temperature; c) preparing a mixture of a precursorsolution and a solvent; d) depositing the mixture of precursor solutionand solvent in the heating chamber to form the solar control coatingcomposed of active n-type protective semiconductor layers deposited onebelow and the other one above a layer of metal nanoparticles having adiameter of less than 30 nm on the recently heated substrate, whereinthe temperature in the heating chamber produces the evaporation of thesolvent and deposits the precursor solution on the substrate surface,forming the solar control coating on the substrate; and e) removing thesubstrate from the clamping area once the coating layer is formed.
 2. Amethod according to claim 1, wherein the step of depositing the mixtureof precursor solution and solvent to form at least one coating layer onthe substrate comprises: producing a micrometric drop cloud or aerosolof the precursor solution on the substrate.
 3. The method according toclaim 2, wherein the micrometric drop cloud is applied with a diameterof between 1 to 20 microns.
 4. The method according to claim 1, whereinthe precursor solution comprises organometallic precursors or inorganiccompounds.
 5. The method according to claim 4, wherein the inorganic ororganometallic precursors are acetates, acetylacetonates, chlorides,nitrates, or halides.
 6. The method according to claim 1, wherein thesolvent being water, distilled water, methanol, ethanol, acetone, or amixture thereof.
 7. The method according to claim 1, wherein thesubstrate temperature is between 100° C. and 600° C.
 8. The methodaccording to claim 1, wherein the concentration of the precursorsolution is from 0.001 to 0.2 mol·dm⁻³.
 9. The method according to claim1, wherein the step of depositing the precursor solution mixture andsolvent of step c) comprises: introducing said mixture into the heatingchamber by means of a carrier gas with a flow of between 1 and 10 Lmin⁻¹.
 10. The method according to claim 9, wherein the carrier gas isair, argon, nitrogen, or a similar gas.
 11. The method according toclaim 1, wherein the step of depositing the mixture of precursorsolution and solvent is performed by the aerosol-assisted chemical vapordeposition technique (AACVD).
 12. The method according to claim 1,wherein the solar control coating comprises: i) a first activeprotective layer residing over one surface of the substrate; ii) anon-continuous metallic nanoparticle layer residing over said firstactive protective layer; iii) a second active protective layer residingover said metallic nanoparticle layer; and iv) a dielectric layer. 13.The method according to claim 12, wherein the non-continuous metallicnanoparticle layer comprises metallic nanoparticles having a diameter ofless than 30 nm.
 14. The method according to claim 12, wherein thedielectric layer comprises Al₂O₃.
 15. The method according to claim 12,wherein the first active protective layer and second active protectivelayer comprise a metal oxide, wherein said metal oxide comprisestitanium or zinc.